1. Field of the Invention
This invention relates to a resonator and a filter including the same for radio equipment and high-frequency measuring instruments.
2. Description of the Prior Art
A resonator which comprises a microwave integrated circuit (MIC) having strip lines is used in an oscillator and a filter employed in high frequency (UHF to SHF) radio equipment. Resonators suited for the microwave integrated circuit are required to be miniaturized and be ungrounded. A split-ring-shaped resonator as such a resonator is disclosed in FIGS. 7(a) to 9(b) of U.S. Pat. No. 4,749,963. This type resonator comprises a ring-shaped strip line and coupling capacity for coupling ends of the ring-shaped strip line. This resonator is capable of largely reducing the length of the strip line less than a half-wave length because the coupling capacitor is provided to the ring-shaped strip line. However, there are drawbacks that dielectric loss in the coupling capacitor tends to deteriorate an unloaded Q factor of the resonator; the dimension of the resonator is still large because there is useless space; there is unevenness of resonance frequencies among resonators manufactured; it is difficult to trim a resonance frequency of the manufactured resonator; and the resonator has a capacitor, increasing manufacturing cost. Similarly, in a filter comprising the above-mentioned resonators, there are drawbacks that dielectric loss in the coupling capacitor of the resonator tends to deteriorate insertion loss of the filter; the dimension of the filter is still large; there is unevenness of resonance frequencies among filters manufactured; it is difficult to trim a resonance frequency of the manufactured resonator of the filter; and the resonators of the filter have a capacitor, increasing manufacturing cost.